Diffusion Toolkit 0.6 includes a new command-line tool called track_merge, which merges multiple track files into one so that one can view them in TrackVis at the same time. Usage is quite simple:
track_merge file1 file2 ... fileN output_file
Requirement for this to work is obvious: all the input track files must have the same geometry information in the header.
A nice thing track_merge does behind the scene is when it merges multiple track files, it does not simply add them. An id type property tag is added to each track in the newly merged file, with each unique id representing where the track was originally from. When the merged file is loaded in TrackVis, a property filter will show up in Track Property panel. Users can adjust that to distinguish and sub-group tracks by its id (origin).